Electrode structure

ABSTRACT

AN ELECTRODE, SUITABLE FOR USE IN AN ANODE ASSEMBLY OF A CELL FOR THE ELECTROLYSIS OF ALKALI METAL HALIDE SOLUTIONS WHICH COMPRISES A MULTI-LAYERED, PLATE-LIKE STRUCTURE, SUBSTANTIALLY RECTANGULAR IN SHAPE. THIS STRUCTURE IS FORMED OF AN INNER PLATE OF AN ELECTRICALLY CONDUCTIVE MATERIAL, SUCH AS ALUMINUM, COPPER, OR IRON. THIS INNER PLATE IS ENCAPSULATED WITHIN TWO OUTER PLATES OF A VALVE METAL, SUCH AS TITANIUM, TANTALUM, OR NIOBIUM. THE TWO OUTER PLATES ARE IDSCONTINUOUSLY BONDED TO THE INNER PLATE BY EFFECTING A FUSION OF THAT PORTION OF THE INNER PLATE AT THE BOND THE THE OUTER PLATE, WITH NO SUBSTANTIAL FUSING OF THE OUTER PLATE. THE EXTERIOR OF THESE OUTER PLATES IS COVERED WITH AN ELECTRICALLY ACTIVE COATING OF A NOBLE METAL, NOBLE METAL ALLOY, NOBLE METAL OXIDE, OR MIXTURES THEREOF.

Sept. 25, 1973 w. w. RUTHEL. ETAL ELECTRODE STRUCTURE Filed June 5o,1971 3 I B h I H v .Wxlxubx xxxxxxxxxxxxxxxx Al lll n :0. HHKHHI||HI|HH\\& 9 9 m 9 r\\ xxxxxxxxxxxxvxxxxxxxxxvccm f) Il a )(H HHHVHH() (W .H 4 ,n N l 5 3 l 'United States Patent O U.S. Cl. 204-290 F 7Claims ABSTRACT F THE DISCLOSURE An electrode, suitable for use in ananode assembly of a' cell for the electrolysis of alkali metal halidesolutions which comprises a multi-layered, plate-like structure,substantially rectangular in shape. This structure is formed of an innerplate of an electrically conductive material, such as aluminum, copper,or iron. This inner plate is encapsulated within two outer plates of avalve metal, such as titanium, tantalum, or niobium. The two outerplates are discontinuously bonded to the inner plate by effecting afusion of that portion of the inner plate at the bond to the outerplate, with no substantial fusing of the outer plate. The exterior ofthese outer plates is covered with an electrically active coating of anoble metal, noble metal alloy, noble metal oxide, or mixtures thereof.

This invention relates to an improved electrode structure, and moreparticularly it`relates to an improved metallic or dimensionally stableelectrode which is suitable for use in an anode assembly of a cell forthe electrolysis of alkali metal halide solutions.

In recent years, considerable development work has been done on metallicor dimensionally stable electrodes, particularly for use as anodes inelectrolytic cells for the production of chlorine, hypochlorites orchlorates by the electrolysis of alkali metal chloride solutions, foruse as anodes for the cathodic protection of iron and steel structuresimmersed in sea water, or for anodes for the electrodialysis of brackishwater, and the like. Although many electrodes of this type have beenproposed, one of the most promising has been an electrode having a baseof a socalled valve metal, such as titanium, and an electrically activecoating of a noble metal, noble metal alloy or noble metal oxide, suchas platinum, ruthenium oxide or the like.

Although from the standpoint of their electrical characteristics andchemical resistance to the conditions encountered in many of theseapplications, electrodes of this type have been generally satisfactory,their adaptai tion for these uses has not been without some problems.Inasmuch as the electrical conductivity of the Valve metals, such astitanium, is relatively low, as compared to materials such as copper oraluminum, the size of these electrodes has been somewhat limited, so asto maintain the electrical operating cost at an -acceptable level.Although attempts have been made to overcome this problem by providingthe titanium electrodes with a core of a more conductive material, suchas copper, diiculties have been encountered in the fabrication ofelectrodes of this type.

It is, therefore, an object of the present invention to provide animproved electrode of the metallic or dimensionally stable type which issuitable for use in an anode assembly of a cell for the electrolysis ofalkali metal halide solutions.

Anotherobject of the present invention is to provide anpimprovevdmetallic electrode of the above type which maybe fabricated' in a widevariety of sizes without sacricing electrical operating eciencies.

A further object of the present invention is to provide an improvedmethod for fabricating metallic or dimensionally stable electrodes.

These and other objects will become apparent to those skilled in the artfrom the description of the invention which follows.

In the drawings which are attached hereto and form a part hereof,

FIG. l is a sectional view of an electrode of the present invention;

FIG. 2 is a plan view of the conductive metal inner core of the presentelectrodes;

FIG. 3 is a plan view of the electrode of the present invention with thetop outer plate removed;

FIG. 4 is a plan view of the assembled electrode of the presentinvention.

Pursuant to the above objects, the present invention includes anelectrode, suitable for use in an anode assembly of a cell for theelectrolysis of alkali metal halide solutions which comprises amulti-layered structure, substantially rectangular in shape, having (l)An inner plate of an electric-ally conductive metal, said plate havingtwo sets of substantially oppositely disposed sides, one side of one ofsaid sets having at least one slot running from the side, in thedirection toward the oppositely disposed side and terminating shortthereof,

(2) Two outer plates of a valve metal selected from titanium, t-antalumand niobium, which plates are disposed on either side of said innerplate, said outer plates being of a size such that they overlap saidinner plate around its entire periphery, said outer plates being bondedto each other around the periphery of said inner plate so as toencapsulate said inner plate, said outer plates further beingdiscontinuously bonded to said inner plate between the slots in saidinner plate and between said slots and the outer edges of said innerplate, said bond being formed by fusion of the portion of the innerplate at the bond to said outer plates with substantially no fusion ofthe outer plates and (3) An electrically active coating on the exteriorof said outer plates, said coating being formed of a noble metal, noblemetal alloy, noble metal oxide or mixtures thereof, wherein said noblemetals are selected from platinum, palladium, ruthenium, rhodium andiridium. It has been found, that the electrodes of the present inventionhave excellent operating characteristics and may be fabricated in a widevariety of sizes without any substantial adverse elfect on thesecharacteristics.

More specifically, the electrodes of the present invention may beutilized in any suitable assembly, such as an anode assembly of a cellfor the electrolysis of alkali metal halide solutions. One particularlysuitable anode assembly of this type is described in a copendingapplication filed of even date herewith, and identified as Ser. No.158,238. These electrodes may, however, be used with various otherassemblies, which provide suitable mounting means, electricalconnections, and the like, depending upon the nature of the environmentin which the electrode is to be used. Although, as has been indicated,these electrodes are particularly adapted for use in the electrolysis ofalkali metal halide solutions, they may also be used, with appropriateassemblies, in other areas, such as for the electrodialysis of brackishwater, the cathodic protection of iron and steel structures immersed insea water, and the like.

The present electrodes are multi-layered, plate-like structures which,desirably, are substantially rectangular in shape. Although theseelectrodes may be fabricated in various other shapes, the substantiallyrectangular shape has been found to be particularly adaptable for mostuses. In general, the overall size of these electrodes will be dictatedby the particular environment in which they are used. It has been found,however, that where solid titanium electrodes have generally beenrestricted to sizes not substantially in excess of about 1 foot by 2feet, because of the high operating costs encountered, due to therelatively high resistance of the titanium where larger sizes are used,the size of the electrodes of the present invention need not be solimited. Thus, with these electrodes, sizes as large as 3 feet by 3feet, 3 feet by 4 feet, 5 feet by 5 feet, or even larger, are feasibleand practical without sacrificing the electrical operating eiiiciencies.It is, therefore, possible when using the electrodes of the presentinvention, to optimize the size and shape of the cell design so as toobtain the maximum production from the cell per square foot of floorspace which it occupys. Additionally, the overall capital investment forcells utilizing these electrodes is also appreciably less than for cellsutilizing solid titanium electrodes.

The present electrode structures are formed of an inner plate of anelectrically conductive material, i.e., a material having an electricalconductivity which is greater than that of the valve metals, such astitanium. Desirably, the inner plate is formed of aluminum, copper,iron, or alloys of these metals, although other metals may be used aswell. In many instances, aluminum has been found to be particularlypreferred as the electrical conductive material, both from thestandpoint of cost and physical properties, although copper or iron ortheir alloys, may also be satisfactorily used.

This inner plate is formed so as to have two sets of substantiallyoppositely disposed sides. In general, the overall dimensions of thisinner plate will be dictated by the desired final dimensions of thefinished electrodes. Similarly, the thickness of this inner plate willbe dictated by not only the desired dimensions of the final finishedelectrode and the particular assembly in which it is to be used, butalso by the strength i.e., rigidity, and the electrical conductivitythat is desired. Typically, where the finished anode is to be used in ananode assembly of a cell for the electrolysis of alkali metal halidesolutions, thicknesses of this inner plate of from about 1/8" to Mi"have been used. These values are merely exemplary, however, as platethicknesses both less than and greater than this range may also be used,depending upon the requirements in each particular application.

This inner plate is formed so that one side of one of the two sets ofsides has at least one slot which runs from the side, in a directiontoward the oppositely disposed side, but terminates short of theoppositely disposed side. Desirably, this inner plate is provided with aplurality of these slots, the particular number being determined,primarily, by the overall size of the plate. In general, it has beenfound to be desirable that a sufficient number of these slots beprovided such that the distance between the slots is not substantiallygreater than about 24 inches. Typically, from about 3 to 5 of theseslots will be used. Although these slots are desirably substantiallyparallel to each other and to one set of oppositely disposed sides andsubstantially perpendicular to the other set of sides, the slots mayalso be formed so as to be non-parallel. Similarly, the length and widthof these slots may vary considerably, with slot lengths which are notsubstantially in excess of about four-fifths of the distance between thetwo sides and slot Widths of from about 1A; to 2 inches, being typical.As with the thickness of this inner plate, however, these values aremerely exemplary of those which may be used.

This inner plate of the electrically conductive material, such asaluminum, is disposed between two outer plates of a valve metal which isselected from titanium, tantalum and niobium. Of these, in manyinstances, the preferred metal has been found to be titanium and forthis reason, hereinafter specific reference will be made to titanium.This is not to be taken as a limitation on the valve metals which may beused, however, since in many instances satisfactory results may also beobtained when using tantalum or niobium.

The two outer plates of titanium are of substantially the same shape asthe inner plate of aluminum and are of a size such that when they aredisposed on either side of the inner aluminum plate, they overlap theinner plate around its entire periphery. Although the amount of thisoverlap should be sufficient to permit the outer plates t0 be bonded toeach other around the periphery of the inner plate, other than beingsufficient to provide for this, the specific amount of the overlap hasnot been found to be critical. By bonding the two outer plates to eachother around the entire periphery of the inner plate, the inner aluminumplate is encapsulated within these outer titanium plates, therebyprotecting it from chemical attack by the solutions in which theelectrodes are used. This bonding of the two outer plates to each othermay be effected in any convenient manner, which will provide for thisencapsulation, such as by resistance welding or the like.

The two outer plates of titanium are discontinuously bonded to the innerplate of aluminum. By discontinuously bonded, it is meant that theplates are not bonded to each other over their entire innerface. Thisbonding of the outer plates to the inner plate is made between the slotsin the inner plate and between the slots and the outer edges of theinner plate. The bond is formed by fusion of that portion of the innerplate at the bond to the outer plates, with substantially no fusion ofthe outer plates. This bonding may be effected by spot-weldingtechniques, or, in a preferred embodiment, by means of a roller seamresistance weld. In either instance, the spot weld or the seam weld aredisposed so as to be between the slots of the inner `aluminum plate andbetween the edge of the inner plate and the slot closest to the edge, ashas been indicated above. Desrably, those bonds do not extend beyond theslots in the aluminum inner plate, which slots terminate short of theone side of the plate, as has been indicated above.

In forming these bonds between the aluminum inner plate and the titaniumouter plates, the welding temperatures used are controlled so as toobtain the fusion of the inner plate at the bond, without effecting anysubstantial fusion of the titanium outer plates. It has been found thatwhere the welding temperatures used are too low, there will beinsuicient melting or fusion of the aluminum plate to effect an adequatebond. Conversely, where the temperatures are too high, there may befusion of the titanium outer plate with the resulting puncture orrupture of the plate, thus permiting corrosion of the aluminum innerplate by the solutions in which the electrodes are used. The bondingwill, thus, be effected by the development of sutiicient heat to locallymelt the aluminum at the point of the application of the heat, withsubstantially no melting or fusion of the titanium, so that upon thesubsequent resolidiication or recrystallization of the aluminum anintimate bond is formed with the titanium.

The electrode structure, having the titanium outer plates bonded to thealuminum inner plate in the manner described above, has, as the linallayer, an electrically active coating on the exterior of the titaniumouter plates. This electrically active coating is formed of a noblemetal, noble metal alloy, noble metal oxide, or mixtures thereof. Thenoble metals in these compositions are selected from platinum,palladium, ruthenium, rhodium and iridium. Particularly, preferredcoatings of this type are the noble metal oxide coatings, such as thosecontaining ruthenium oxide. These electrically active coatings may beapplied to the exterior of the titanium outer plates in any convenientmanner. Typical of the application techniques which may be used, as areknown to those in the art, are electrolytic applications, including bothelectroplating and electrophoretic deposition, vapor phase depositions,electroless plating, as well as various cladding techniques, and thelike. Typically, the electrically active coating will be of a thicknessof from about 4 to 60 microinches, although in many instances bothgreater and lesser thicknesses may be used.,In general, however, becauseof the cost of such coating materials, it is preferred to utilize asthin a coating as possible, consistent with aV reasonable economic life.Y

Referring now to the drawing, as is shown in FIG. 1, which is asectional view of the electrode of the present invention, this electrodeis formed of an inner core or plate 1, two outer plates 3 and 4 and anouter layer 5 on the outside of the outer plates 3 and 4. The innerplate 1 is of an electrically conductive material such as aluminum,copper, iron, and alloys thereof, with aluminum being preferred. Theouter plates 3 and 4 are formed of a valve metal, with titanium beingpreferred. The outer coating 5 on the plates 3 and 4 is of anelectrically active material such as a noble metal, noble metal alloy,noble metal oxide and mixtures of these, which coatings containingruthenium oxide being preferred. The plates 3 and 4 are bonded to eachother preferably by welding, as is shown at 7.

Referring now to FIGS. 2 and 3, the aluminum inner plate 1 issubstantially rectangular in shape and has two sets of substantiallyoppositely disposed sides 9 and 11 and 13 and 15. Side 11 has aplurality of slots 17 formed therein, which slots run from side 11toward the oppositely disposed side 9, but terminate short of this side.Although these slots are desirably substantially parallel to each otherand to sides 13 and 1S and substantially perpendicular to sides 11 and9, they may be positioned in a non-parallel relationship, e.g., in afan-like shape.

As is shown in FIG. 3, the aluminum inner plate 1 is placed on atitanium outer plate 3, which latter plate is of substantially the sameshape as plate 1. The size of plate 3, however, is such that it overlapsplate 1 around its entire periphery. As is shown in FIG. 4, the secondtitanium outer sheet 4 is placed on top of the assembly shown in FIG. 3and the entire assembly is bonded together. The titanium outer sheets 3and 4 are discontinuously bonded to the aluminum inner sheet 1 by meansof seam welds 19. These welds 19 are made between the slots 17 of thealuminum inner plate 1 and also between the outer edges 15 and 13 ofsheet 1 and the slots closest to these edges. Additionaly, the titaniumouter sheets 3 and 4 are bonded to each other by means of the Weld 7which is around the entire periphery of the electrode. The exteriorsurfaces of the titanium outer plates are then coated with theelectrically active coating material 5, as shown in FIG. 1. It is to beappreciated that although, in IFIG. 4, the titanium outer sheets 3 and 4are shown as being bonded to the aluminum inner sheet 1 by means of theseam welds 19, these seam welds may be replaced by a series of spotwelds, positioned in the same relative areas, if desired.

In fabricating the electrodes of the present invention, a plate or sheetof aluminum or other electrically conductive material is formed into thedesired substantially rectangular shape and slotted in the manner shownin FIG. 2. Thereafter, the slotted aluminum plate is placed between twoouter plates of titanium or a similar valve metal, which outer platesare of a size such that they overlap the inner aluminum plate around itsentire periphery. The outer titanium plates are then bonded to the inneraluminum plate by resistance welding the titanium-aluminum-titaniumsandwich to form a seam weld between the slots in the aluminum plate andbetween the edge of the aluminum plate and the slots closest to theedge. As has been indicated, this welding is carried out at temperaturessuch that there is a melting or fusion of the aluminum, withoutsubstantial melting or fusion of the titanium. In this manner, there isone bond between the aluminum and titanium in each section or finger ofthe aluminum plate and it is through these bonds that the electricalconductivity between the aluminum and titanium is effected.

Thereafter, the two outer titanium plates or sheets are bonded to eachother around the entire periphery, preferably by resistance welding, soas to encapsulate the alumi- A num inner plate within a titaniumenvelope, thus forming a leakproof, modular unit in which the aluminumis protected from vthe corrosive action of the solutions in which theelectrodes are used. This sealed unit is then coated on its exteriorsurfaces With an electrically active coating, the preferred coatingbeing a mixture of noble metal oxides, which includes ruthenium oxide.In a preferred embodiment, this electrically active coating of noblemetal oxides is deposited on the exterior of the titanium outer platesby means of electrophoretic deposition from a dispersion of the noblemetal oxides in a solvent. Other coating techniques, as are known tothose in the art, may also be used, depending upon the particularelectrically active coating which is desired.

The electrodes of the present invention, fabricated in the manner as hasbeen set forth hereinabove, have been found to have excellent electricalcharacteristics, exhibiting an appreciably lower voltage drop in usethan do coated, solid titanium electrodes of the same size. Moreover, bybonding the inner and outer plates of this electrode to each other inthe manner which has been described, there has been found to berelatively little physical distortion of the electrode duringfabrication. Itis, therefore, feasible to fabricate these electrodes inrelatively larger sizes than has been heretofore possible with solidtitanium electrodes, while still maintaining the necessary physicaltolerances and the overall electrode assembly and without sacrificingthe electrical characteristics, e.g., without encountering unacceptablevoltage drops.

While there have been described various embodiments of the invention,the compositions and methods described are not intended to be understoodas limiting the scope of the invention as it is realized that changestherewithin are possible and it is further intended that each elementrecited in any of the following claims is to be understood as referringto all equivalent elements for accomplishing substantially the sameresults in substantially the same or equivalent manner, it beingintended to cover the invention broadly in whatever form its principlemay `be utilized.

What is claimed is:

1. An electrode, suitable for use in an anode assembly of a cell for theelectrolysis of alkali metal halide solutions, which comprises amulti-layered structure having (l) an inner plate of an electricallyconductive metal,

said inner plate having two sets of substantially oppositely disposedsides, one side of one of said sets having a plurality of slots runningfrom the side, in the direction toward the oppositely disposed side andterminating short thereof,

(2) two outer plates of a valve metal selected from titanium, tantalumand niobium, which plates are disposed on either face of said innerplate, said outer plates being of the size such that they overlap saidinner plate around its entire periphery, said outer plates being `bondedto each other around the periphery of said inner plate so as toencapsulate said inner plate, said outer plates further beingdiscontinuously bonded to said inner plate by a plurality of bondsdisposed only between the slots in said inner plate and between saidslots and the outer edges of said inner plate, the width of said bondsbeing less than the width of the spaces between said slots and the widthof the spaces between said slots and the outer edges of said inner plateand the length of said bonds being such that the bonds do not extendbeyond said slots, said bonds further being formed by fusion of theportion of the inner plate at the bond to said outer plates withsubstantially no fusion of the outer plates and (3) an electricallyactive coating on the exterior of said outer plates, said coating beingformed on a noble metal, noble metal alloy, noble metal oxide ormixtures thereof, wherein said noble metals are selected from platinum,palladium, ruthenium, rhodiumY and iridium.

2. The electrode as claimed in claim 1 wherein the inner and outerplates are substantially rectangular in shape.

Y 3. The electrodes as claimed in claim 2 wherein the slots aresubstantially parallel to each other and to oneset of sides of saidplates.

4. The electrode as claimed in claim 3 wherein the discontinuous bondbetween the inner plate and the outer plates is a resistance weldedseam.

5. The electrode as claimed in claim 3 wherein the discontinuous bondbetween the inner plate and outer plates is a series of spot welds.

6. The electrode as claimed in claim 4 wherein the inner plate isselected from aluminum, copper, iron and alloys thereof.

7. The electrode as claimed in claim 6 wherein the inner plate isaluminum, the outer plates are titanium, and the electrically activecoating is a noble metal oxide'coating containing ruthenium oxide.

A References Cited UNITED STATES PATENTS.

3,380,908 Ono et al. 204-290 F OTHER REFERENCES n Der-Pub. 689,485,March 1969, Tr, T 860.019.

U.S. Cl. X.R.

